1. Field of the Invention
The present invention relates to an inkjet recording apparatus which records an image on a recording medium by discharging ink from a recording head thereof, and a recording position adjustment method therefor.
2. Description of the Related Art
Conventionally, as a technique used in an inkjet recording apparatus, there has been known the technique of correcting a deviation of a dot-recorded position (a position where an ink droplet is placed) on a recording medium. Japanese Patent Application Laid-Open No. 11-240146 discusses the technique for controlling ink discharge timing according to the position of a carriage with a recording heat loaded thereon in a scanning direction, thereby accurately correcting a recording position regardless of where the carriage is located in the scanning position even when there is a variation in the distance between the carriage and the recording medium in the scanning direction.
However, an amount of deviation of ink droplet impact position varies within the scanning range of the carriage not only in a case of deviations in the scanning direction but also in a case of deviations in the direction intersecting the scanning direction (conveyance direction). One of the causes thereof is, for example, a change in the posture of the carriage during the scanning operation.
FIG. 15 schematically illustrates a change in the posture of the carriage. FIG. 15 illustrates a main rail 8, a sub rail 6, a carriage 4, a recording head 1, and a recording position deviation 23. For example, if the main rail 8 is slightly crooked, the carriage 4 in one position has such a posture that the carriage 4 is inclined relative to a platen as indicated by the diagonal line, while the carriage 4 in another position has such a posture that the carriage 4 is in parallel with the platen. The recording head 1 loaded on the carriage 4 includes a plurality of nozzle arrays arranged at different positions in the scanning direction. When the respective nozzle arrays record dots on a same position on a recording medium, their discharge timing varies for each nozzle array by a time corresponding to the distance between the nozzle arrays and the carriage scanning speed. This means that the carriage is located at different positions in the scanning direction when two nozzle arrays discharge ink to record dots on the same position on the recording medium and the carriage may have different postures at each discharge timing. In this way, the different postures of the carriage result in a deviation in the conveyance direction as to dot-recorded positions which are supposed to be a same position.
A deviation of an impact position in the scanning direction can be corrected by adjustment of the discharge timing, and therefore it is possible to set adjustment values for respective positions within the scanning range. However, for correcting a deviation of an impact position in the conveyance direction, either data should be shifted in the conveyance direction or the nozzle use range should be changed, therefore it is desirable to use one adjustment value to keep the impact position deviation within the required accuracy range throughout the entire scanning range.
When an impact position deviation in the conveyance direction is adjusted at a recording apparatus equipped with a recording head with three or more nozzle arrays formed thereon, a specific nozzle array is set as a reference array, and an adjustment value is applied to each of other nozzles. For example, it is assumed that there is a reference nozzle array, and a nozzle array A and a nozzle array B are the other nozzle arrays. In this case, optimal adjustment of the impact position of the nozzle array A in the conveyance direction relative to the reference nozzle array may result in a further increased deviation between the impact positions of the nozzle arrays A and B. However, the deviation between the nozzle arrays A and B may have a greater influence on the image than the deviation between the reference nozzle array and the nozzle array A. In this case, the adjustment value to the deviation between the nozzle arrays A and B should be preferentially optimally set. Therefore, when adjustment values for nozzle arrays are determined at a recording apparatus equipped with three or more nozzle arrays, the adjustment values should be determined in consideration of the priority order of those nozzle arrays.